ServiceWorker: statechange 事件
注意：此功能在 Web Workers 中可用。
当 ServiceWorker.state 发生变化时，就会触发 statechange 事件。
语法
在诸如 addEventListener() 之类的方法中使用事件名称，或设置事件处理程序属性。
js
addEventListener("statechange", (event) => { })
onstatechange = (event) => { }
事件类型
一个通用的 Event。
示例
此代码片段来自 service worker registration-events 示例（实时演示）。代码会监听 ServiceWorker.state 的任何变化并返回其值。
js
let serviceWorker;
if (registration.installing) {
serviceWorker = registration.installing;
document.querySelector("#kind").textContent = "installing";
} else if (registration.waiting) {
serviceWorker = registration.waiting;
document.querySelector("#kind").textContent = "waiting";
} else if (registration.active) {
serviceWorker = registration.active;
document.querySelector("#kind").textContent = "active";
}
if (serviceWorker) {
logState(serviceWorker.state);
serviceWorker.addEventListener("statechange", (e) => {
logState(e.target.state);
});
}
请注意，当 statechange 触发时，service worker 的引用可能已经改变。例如
js
navigator.serviceWorker.register("/sw.js").then((swr) => {
swr.installing.state = "installing";
swr.installing.onstatechange = () => {
swr.installing = null;
// At this point, swr.waiting OR swr.active might be true. This is because the statechange
// event gets queued, meanwhile the underlying worker may have gone into the waiting
// state and will be immediately activated if possible.
};
});
规范
| 规范 |
|---|
| Service Workers # dom-serviceworker-onstatechange |
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